Abstract: A sphere moving down a bumpy incline in the air is studied theoretically and experimentally. A method based on the principle of energy conservation is used to express the average velocity of a sphere moving down the incline without any acceleration or deceleration. Two empirical coefficients in the theoretical expression of the average velocity of a sphere were determined by experiments. Using this theoretical average velocity, one can compute and then compare the collision and non-collision parts of the shear stress exerted on the interface between the moving sphere and the bumpy incline.